Howdy, do any of the standard included Finale fonts include the Hauptstimme (or Nebenstimme) abbreviation symbols? I peeked through the viewer and found nothing, but just because I didn't find it does not mean it isn't there...

There are indeed no symbols for H (U+1D1A6) or N in standard Finale fonts.
But some fonts do have it, such as Sonora, Stockholm, Fravura Extra, Opus Extra, FreeSerif, Thesis, Bravura.
You can also create it in Finale shape designer, by typing N and add a line to get it correctly.